What is IP address?

Just like your real life mail address used to receive Amazon package, IP address (Internet Protocol address) is a label to mark your
location in the Internet, so other computers (mostly website servers) know where
to send the data.

There are two kinds of IP address. Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6). IPv6 used a
128 bits number to mark your location, though IPv6 will not be used widely in
next 10 years. IPv4 used a 32 bits number to mark your location (0.0.0.0 ~ 255.255.255.255), which means it has totally
2^32 = 4,294,967,296 unique address. (4 billion is not a large
number !!!).

Most likely, the device you are using right now, doesn't has a unique IPv4 public address, however, a private address is used. Your
router has a dedicate public IP address and works as a pub to
transit all the Internet traffic to the outside world. This technology is called NAT (Network address translation). NAT can not only
save IPv4 address, but also provide you an extra layer of security
protection.

Why should I care about IP address?

Privacy. Your IP address might expose your real geographical information (which country and which city). VPN or proxy is often used
by people who wants to change his/her Internet location. It's a trade off between
which authority do you trust more, your IPS (Internet Service Provider) is national large companies that work with government. On
the other hand, VPN providers build their business based on protect its
customer's privacy but you didn't know for sure whether they collect your browsing history. For advanced users, I suggest using Tor,
one VPN tunnel following by another VPN tunnel. So no one can know your real IP
address.